N-heterocyclyl hydrazides as neurotrophic agents

ABSTRACT

This invention relates to a series of N-heterocyclyl hydrazides of Formula I,  
                 
 
     and pharmaceutical compositions containing them. The compounds of the invention have neurotrophic activity and are useful in the treatment and prevention of neuronal disorders such as Parkinson&#39;s disease, Alzheimer&#39;s disease, stroke, multiple sclerosis, amyotrophic lateral sclerosis diabetic neuropathy and Bell&#39;s palsy.

FIELD OF THE INVENTION

[0001] This invention relates to certain novel N-heterocyclyl hydrazideshaving neurotrophic activity. These compounds, along with relatedcompositions and methods, are useful in the treatment and prevention ofneuronal disorders such as Parkinson's disease, Alzheimer's disease,stroke, multiple sclerosis, amyotrophic lateral sclerosis, diabeticneuropathy, and Bell's palsy.

BACKGROUND OF THE INVENTION

[0002] This application claims priority from U.S. provisionalapplication No. 60/327,019 filed Oct. 4, 2001 and entitled“N-heterocyclyl Hydrazides as Neurotrophic Agents” the contents of whichare hereby incorporated by reference in their entirety.

[0003] Neurodegenerative diseases constitute a major threat to publichealth throughout the world. One of the most serious of such diseases isAlzheimer's disease (AD), a major cause of dementia in aged humans andthe fourth most common medical cause of death in the United States. Inthe U.S., it is estimated that AD afflicts two to three millionindividuals overall, and more than 5% of the population over the age of65. Although the exact etiology of AD remains to be defined, the diseaseis characterized by the presence of a large number of amyloid plaquesand neurofibrillary tangles in regions of the brain involved incognitive function, and degeneration of cholinergic neurons that ascendfrom the basal forebrain to cortical and hippocampal areas. Currently,there are no effective therapies for AD (Brinton, R. D. and Yamazaki, R.S., Pharm. Res., 1998, 15:386-98).

[0004] Similar to AD, Parkinson's Disease (PD) is a progressivedegenerative disease of the central nervous system (CNS). The lifetimeincidence of the disease is approximately 2% in the general population.In PD, degeneration of the dopaminergic neurons of the substantia nigraleads to a decrease in dopamine levels in the region of the braincontrolling voluntary movement, the corpus striatum. Therefore, standardtreatments have focused on the administration of agents, like L-dopa andbromocriptine, which replenish dopamine levels in the affected areas ofthe brain. Dopaminergic regimens lose their efficacy, however, as nervecells continue to die and the disease progresses. At the same time theinvoluntary tremors seen in the early stages of PD advance to periods ofdifficult movement and, ultimately, to immobility. Therefore,alternative therapies are actively being sought (Pahwa, R. and Koller,W. C., Drugs Today, 1998, 34:95-105).

[0005] Neurodegenerative diseases of the somatosensory nervous systemalso constitute a class of debilitating and potentially lethalconditions. Amyotrophic lateral sclerosis (ALS) is a fatal diseasecharacterized by progressive degeneration of the upper and lower motorneurons. Although the precise etiology of ALS is unknown, populartheories suggest that excitotoxicity and/or oxidative stress arecontributing factors. Riluzole is the first drug approved and marketedfor ALS. It possesses antiexcitotoxic properties and has been shown toincrease the rate of survival of ALS patients. However, the drug is nota cure, and clinical trials of alternative agents are currently underway(Louvel, E., Hugon, J. and Doble, A., Trends Pharmacol. Sci., 1997,18:196-203).

[0006] Peripheral neuropathies are secondary to a number of metabolicand vascular conditions. In particular, approximately 30% of patientswith diabetes mellitus suffer from some form of peripheral neuropathythat may affect the small myelinated fibers, causing loss of pain andtemperature sensation, or the large fibers, causing motor orsomatosensory defects. Pharmacotherapeutic intervention tends to besymptomatic, and the best approach to treatment and prevention remainsthe maintenance of normal blood glucose levels through diet and insulinadministration (Biessels, G. J. and Van Dam, P. S., Neurosci. Res.Commun., 1997, 20:1-10).

[0007] A considerable body of evidence now suggests that deficiencies inthe levels of certain proteinaceous growth factors, or neurotrophicfactors, may play key pathoetiological roles in both peripheral andcentral neurodegenerative diseases (Tomlinson et al., Diabetes, 1997,46(suppl. 2):S43-S-49; Hamilton, G. S., Chem. Ind., (London) 1998,4:127-132; Louvel et al., Trends Pharmacol. Sci., 1997, 18:196-203;Ebadi et al., Neurochem. Int., 1997, 30:347-374).

[0008] These neurotrophic factors can be divided into two structuralclasses: 1) the neurotrophins, including nerve growth factor (NGF);glial cell-derived neurotrophic growth factor (GDNF); brain-derivedneurotrophic factor (BDNF); neurotrophin 3 (NT-3); neurotrophin 4/5(NT-4/5); neurotrophin 2 (NT-2); and ciliary neurotrophic factor (CNTF)which is related to the cytokine family of molecules. All neurotrophicfactors promote neurite outgrowth, induce differentiation, and suppressprogrammed cell death or apoptosis in specific subpopulations ofperipheral and central neurons. For example, NGF exerts trophic effectson sympathetic and sensory neurons of the dorsal root ganglion andcholinergic neurons of medial septum in the CNS, suggesting potentialtherapeutic utility in AD. CNTF has trophic actions on a broadcross-section of neurons, including parasympathetic, sensory,sympathetic, motor, cerebellar, hippocampal, and septal neurons. Ofparticular interest is the fact that CNTF partially prevents the atrophyof skeletal muscle following the formation of nerve lesions but has noeffect on innervated muscle, indicating that CNTF is primarily operativein the pathological state. As a result, CNTF is currently beingevaluated for its effects in musculoskeletal diseases like ALS.

[0009] The clinical utility of proteinaceous neurotrophic agents isseverely hampered by their limited bioavailability, especially in theCNS. This necessitates the administration of these agents directly intothe brain to induce a therapeutic effect. Direct introduction of agentsinto the brain is a relatively hazardous and cumbersome route ofadministration.

[0010] Protein based compounds currently in clinical use as neurotrophicagents cannot be administered orally and otherwise show poorbioavailability except when administered intracerebroventricularly,“ICV,” for a CNS indication or intravenously for peripheral nervedysfunctions such as diabetic neuropathy or Bell's palsy. Accordingly,there is a clear need for bioavailable small molecule mimetics ofneurotrophic factors that are orally bioavailable and can readilypenetrate the blood-brain barrier.

[0011] Great efforts have been made to identify small molecules havingneurotrophic activity, but all such compounds reported so far arestructurally dissimilar to N-heterocyclyl hydrazides.

SUMMARY OF THE INVENTION

[0012] This invention provides novel N-heterocyclyl hydrazides havingsurprising neurotrophic activity. Demonstrated to have these biologicalactivities by in vitro and in vivo assays described hereinafter are thecompounds of the present invention as shown in Formula I:

[0013] or a pharmaceutically acceptable salt thereof, wherein

[0014] H₁ is selected from the group consisting of a 4-memberednitrogen-containing heterocyclyl having 3 carbon ring atoms, a5-membered nitrogen-containing heterocyclyl having 0 or 1 additionalheteroatom ring member selected from O, S, and N, and a 6- or 7-memberednitrogen-containing heterocyclyl having 0, 1, or 2 additional heteroatomring members selected from O, S, and N;

[0015] H₂ is a 5- or 6-membered heteroaryl;

[0016] R₁ is selected from urea, C₁-C₁₀ alkyl, aryl, heteroaryl,heterocyclyl, —C(O)R, —C(O)—C(O)R, —SO₂R, and —P(O)(OR′)(OR″), whereinR, R′, and R″ are independently selected from alkyl, aryl, heteroaryl,and heterocyclyl; and

[0017] R₂ and R₃ are independently hydrogen or C₁-C₁₀ alkyl.

[0018] This invention also provides a pharmaceutical compositioncomprising the instant compound and a pharmaceutically acceptablecarrier, as well as related synthetic methods.

[0019] This invention further provides a method of treating a subjectsuffering from a condition characterized by neuronal damage caused bydisease or trauma, which method comprises administering to the subject atherapeutically effective dose of the instant pharmaceuticalcomposition.

[0020] This invention still further provides a method of inhibiting in asubject the onset of a condition characterized by neuronal damage causedby disease or trauma, which method comprises administering to thesubject a therapeutically effective dose of the instant pharmaceuticalcomposition.

DETAILED DESCRIPTION OF THE INVENTION

[0021] This invention provides novel triazepine compounds havingsurprising neurotrophic activity. These compounds, along with relatedpharmaceutical compositions and methods, are useful in the treatment andprevention of neuronal disorders including, for example, Parkinson'sdisease, Alzheimer's disease, stroke, multiple sclerosis, amyotrophiclateral sclerosis, diabetic neuropathy or Bell's palsy. They are alsouseful in the treatment of disorders caused by trauma to the brain,spinal cord or peripheral nerves.

[0022] Specifically, this invention provides a compound of Formula I,

[0023] or a pharmaceutically acceptable salt thereof, wherein

[0024] H₁ is selected from the group consisting of a 4-memberednitrogen-containing heterocyclyl having 3 carbon ring atoms, a5-membered nitrogen-containing heterocyclyl having 0 or 1 additionalheteroatom ring member selected from O, S, and N, and a 6- or 7-memberednitrogen-containing heterocyclyl having 0, 1, or 2 additional heteroatomring members selected from O, S, and N;

[0025] H₂ is a 5- or 6-membered heteroaryl;

[0026] R₁ is selected from urea, C₁-C₁₀ alkyl, aryl, heteroaryl,heterocyclyl, —C(O)R, —C(O)—C(O)R, —SO₂R, and —P(O)(OR′)(OR″), whereinR, R′, and R″ are independently selected from alkyl, aryl, heteroaryl,and heterocyclyl; and

[0027] R₂ and R₃ are independently hydrogen or C₁-C₁₀ alkyl.

[0028] More specifically, this invention provides a compound of FormulaIa,

[0029] wherein H_(2a) is a 5- or 6-membered heteroaryl wherein X is aheteroatom selected from O, S, and N, and R₁, R₂, R₃, and H₁ are asdescribed above.

[0030] More specifically, this invention provides a compound of FormulaIb,

[0031] wherein R₁, R₂, R₃, H₁, and H₂ are as described above.

[0032] In one embodiment of the instant compound, R₁ is selected fromthe group consisting of —C(O)R, —C(O)—C(O)R, and —SO₂R wherein R isselected from the group consisting of aryl, heteroaryl, cycloalkyl, andC₄-C₁₀ straight or branched alkyl. In another embodiment, H₂ is apyridine. In yet another embodiment, R₂ and R₃ are independently C₁-C₅alkyl. In still another embodiment, R₁ is selected from C₄-C₁₀ alkyl,aryl, heteroaryl, and heterocyclyl.

[0033] Unless specified otherwise, the term “alkyl” refers to astraight, branched or cyclic substituent consisting solely of carbon andH with or without unsaturation, optionally substituted with one or moreindependent groups including, but not limited to, halogen, OH, amino,alkoxy, aryl, substituted aryl, heteroaryl, substituted heteroaryl,heterocyclyl, and substituted heterocyclyl. The term “alkoxy” refers toO-alkyl where alkyl is as defined supra. The term “halo” or “halogen”means fluoro, chloro, bromo or iodo.

[0034] The term “aryl” or “aromatic ring” refers to a 5- to 6-memberedring containing a 6-electron delocalized conjugated pi bonding systemsuch as phenyl, furanyl, and pyrrolyl. The term “aryl” or “aromaticring” includes mono and fused aromatic rings such as phenyl, naphthyl,diphenyl, fluorophenyl, difluorophenyl, benzyl, benzoyloxyphenyl,carboethoxyphenyl, acetylphenyl, ethoxyphenyl, phenoxyphenyl,hydroxyphenyl, carboxyphenyl, trifluoromethylphenyl, methoxyethylphenyl,acetamidophenyl, tolyl, xylyl, dimethylcarbamylphenyl and the like. Thesymbol “Ph” refers to phenyl.

[0035] The term “heteroaryl” as used herein represents a stable five orsix-membered monocyclic or bicyclic aromatic ring system which consistsof carbon atoms and from one to three heteroatoms selected from N, O andS. The heteroaryl group may be attached at any heteroatom or carbonatom, which results in the creation of a stable structure. Examples ofheteroaryl groups include, but are not limited to pyridinyl, pyrazinyl,pyridazinyl, pyrimidinyl, thiophenyl, furanyl, imidazolyl, isoxazolyl,oxazolyl, pyrazolyl, pyrrolyl, thiazolyl, thiadiazolyl, triazolyl,benzimidazolyl, benzofuranyl, benzothienyl, benzisoxazolyl,benzoxazolyl, benzopyrazolyl, indolyl, benzothiazolyl,benzothiadiazolyl, benzotriazolyl or quinolinyl.

[0036] Unless specified otherwise, aryl or heteroaryl may be substitutedby one to three independent groups such as halogen, aryl, heteroaryl,OH, CN, mercapto, nitro, C₁₋₁₀-alkyl, halo-C₁₋₁₀-alkyl, CF₃,C₁₋₁₀-alkoxy, C₁₋₁₀-alkylthio, amino, C₁₋₁₀-alkyl-amino,di(C₁-C₈-alkyl-)amino, arylamino, nitro, formyl, carboxyl,alkoxycarbonyl, C₁₋₁₀-alkyl-CO—O—, C₁₋₁₀-alkyl-CO—NH—, and carboxamide.The substituted heteroaryl may also be substituted with a substitutedaryl or a second substituted heteroaryl to give, for example, a2-phenylpyrimidine or a 2-(pyrid-4-yl)pyrimidine, and the like. Unlessspecified otherwise, the terms “substituted aryl” and “substitutedheteroaryl” include aryl and heteroaryl that are fused with one or more3- to 8-membered cycloalkyl or 5- to 7-membered ring systems selectedfrom the group consisting of aryl, heteroaryl, and heterocyclyl.

[0037] “Heterocyclyl” or “heterocycle” is a 3- to 8-member saturated orpartially saturated, single or fused ring system which consists ofcarbon atoms and from one to four heteroatoms selected from N, O and S.Unless specified otherwise, the heterocyclyl group may be attached atany heteroatom or carbon atom which results in the creation of a stablestructure. Examples of heterocyclyl groups include, but are not limitedto, pyridine, pyrimidine, oxazoline, pyrrole, imidazole, morpholine,furan, indole, benzofuran, pyrazole, pyrrolidine, piperidine, andbenzimidazole. The “heterocyclyl” or “heterocycle” may be substitutedwith one or more independent groups including, but not limited to, H,halogen, oxo, OH, C₁-C₁₀ alkyl, CF₃, amino, and alkoxy. Unless specifiedotherwise, substituted heterocyclyl includes heteroaryl fused with oneor more 3- to 8-membered cycloalkyl or 5- to 7-membered ring systemsselected from aryl, heteroaryl, and heterocyclyl.

[0038] The instant compounds can be isolated and used as free bases.They can also be isolated and used as pharmaceutically acceptable salts.The phrase “pharmaceutically acceptable salt” denotes salts of the freebase which possess the desired pharmacological activity of the free baseand which are neither biologically nor otherwise undesirable. Thesesalts may be derived from inorganic or organic acids. Examples ofinorganic acids are hydrochloric acid, hydrobromic acid, hydroiodicacid, perchloric acid, nitric acid, sulfuric acid and phosphoric acid.Examples of organic acids are acetic acid, propionic acid, glycolicacid, lactic acid, pyruvic acid, malonic acid, succinic acid, malicacid, maleic acid, maleic acid, fumaric acid, tartaric acid, citricacid, benzoic acid, cinnamic acid, mandelic acid, oxalic acid, pamoicacid, saccharic acid, methanesulfonic acid, ethanesulfonic acid,p-toluenesulfonic acid, methyl sulfonic acid, salicyclic acid,hydroethanesulfonic acid, benzenesulfonic acid, 2-naphthalenesulfonicacid, p-toluenesulfonic acid, cyclohexanesulfamic acid and the like.Alternatively, “pharmaceutically acceptable salt” denotes salts of thefree acid which possess the desired pharmacological activity of the freeacid and which are neither biologically nor otherwise undesirable. Thesesalts may be derived from a metal ion or an organic base, such as Li,Na, K, NH₄ and the like.

[0039] Where the compounds according to this invention have one or morestereogenic centers, it is to be understood that all possible opticalisomers, antipodes, enantiomers, and diastereomers resulting fromadditional stereogenic centers that may exist in optical antipodes,racemates and racemic mixtures thereof are also part of this invention.The antipodes can be separated by methods known to those skilled in theart such as, for example, fractional recrystallization of diastereomericsalts of enantiomerically pure acids. Alternatively, the antipodes canbe separated by chromatography in a Pirkle-type column.

[0040] Some of the crystalline forms for the compounds may exist aspolymorphs and as such are intended to be included in the presentinvention. In addition, some of the compounds may form solvates withwater (i.e., hydrates) or common organic solvents, and such solvates arealso intended to be encompassed within the scope of this invention.

[0041] The following compounds are exemplary of the present invention:

[0042] In one embodiment, the compound of the invention is selectedfrom:

[0043] 1-(3,3-dimethyl-2-oxo-pentanoyl)-pyrrolidine-2-carboxylic acidN′-pyridine-2-yl-hydrazide;

[0044] 1-(2-oxo-2-thiophen-2-yl-acetyl)piperidine-2-carboxylic acidN′-(6-methyl-4-trifluoromethyl-pyridin-2-yl)-hydrazide; and

[0045] 2-azetidinecarboxylic acid, 1-[(phenylmethyl)sulfonyl]-,2-(2-pyridinyl)hydrazide, (2S)-.

[0046] This invention also provides a pharmaceutical compositioncomprising the instant compound and a pharmaceutically acceptablecarrier.

[0047] Pharmaceutical compositions containing the compound of thepresent invention as the active ingredient in intimate admixture with apharmaceutical carrier can be prepared according to conventionalpharmaceutical techniques. The carrier may take a wide variety of formsdepending on the form of preparation desired for administration, such astopical administration and systemic administration including, but notlimited to, intravenous infusion, oral, nasal or parenteral. Inpreparing the compositions in oral dosage form, any of the usualpharmaceutical carriers may be employed, such as water, glycerol,glycols, oils, alcohols, flavoring agents, preservatives, coloringagents, syrup and the like in the case of oral liquid preparations (forexample, suspensions, elixirs and solutions); or carriers such asstarches, sugars, methyl cellulose, magnesium sterate, dicalciumphosphate, mannitol and the like in the case of oral solid preparations(for example, powders, capsules and tablets). All excipients may bemixed as needed with disintegrants, diluents, granulating agents,lubricants, binders and the like using conventional techniques known tothose skilled in the art of preparing dosage forms.

[0048] The preferred route of administration is oral administration.Because of their ease in administration, tablets and capsules representan advantageous oral dosage unit form, in which case solidpharmaceutical carriers are obviously employed. If desired, tablets maybe sugar-coated or enteric-coated by standard techniques. Forparenterals, the carrier will usually comprise sterile water, thoughother ingredients, for example, to aid solubility or for preservativepurposes, may be included. Injectable suspensions may also be prepared,in which case appropriate liquid carriers, suspending agents and thelike may be employed.

[0049] This invention also provides a method of stimulating neuronalgrowth comprising contacting neurons with an effective amount of theinstant compound. The contacting step can be performed, for example, invitro, ex vivo or in vivo.

[0050] The compounds of the present invention stimulate neuronal growth.Thus, this invention further provides a method of treating a subjectsuffering from a condition characterized by neuronal damage caused bydisease or trauma, which method comprises administering to the subject atherapeutically effective dose of the instant pharmaceuticalcomposition. As used herein, the term “subject” includes, withoutlimitation, any animal or artificially modified animal. In the preferredembodiment, the subject is a human.

[0051] In one embodiment, the disorder treated is caused by disease, andis selected from the group consisting of Parkinson's disease,Alzheimer's disease, stroke, multiple sclerosis, amyotrophic lateralsclerosis, peripheral neuropathy and Bell's palsy. In anotherembodiment, the disorder treated is caused by trauma to the brain,spinal cord or peripheral nerves.

[0052] This invention still further provides a method of inhibiting in asubject the onset of a condition characterized by neuronal damage causedby disease or trauma, which method comprises administering to thesubject a prophylactically effective dose of the instant pharmaceuticalcomposition.

[0053] In one embodiment, the condition is selected from the groupconsisting of Parkinson's disease, Alzheimer's disease, stroke, multiplesclerosis, amyotrophic lateral sclerosis, peripheral neuropathy andBell's palsy. In the preferred embodiment, the condition is Alzheimer'sdisease.

[0054] As used herein, “treating” a disorder means eliminating,reducing, limiting, or otherwise ameliorating the cause and/or effectsthereof. “Inhibiting” the onset of a disorder means preventing, delayingor reducing the likelihood of such onset. Likewise, “therapeuticallyeffective” and “prophylactically effective” doses are doses that permitthe treatment and inhibition, respectively, of a disorder.

[0055] Methods are known in the art for determining therapeutically andprophylactically effective doses for the instant pharmaceuticalcomposition. The effective dose for administering the pharmaceuticalcomposition to a human, for example, can be determined mathematicallyfrom the results of animal studies.

[0056] In one embodiment, oral doses of the instant compounds range fromabout 0.01 to about 200 mg/kg, daily. In another embodiment, oral dosesrange from about 0.1 to about 50 mg/kg daily, and in a furtherembodiment, from about 1 to about 30 mg/kg daily. Infusion doses canrange, for example, from about 1.0 to 1.0×10⁴ μg/kg/min of instantcompound, admixed with a pharmaceutical carrier over a period rangingfrom several minutes to several days. For topical administration, theinstant compound can be mixed with a pharmaceutical carrier at aconcentration of, for example, about 0.1 to about 10% of drug tovehicle.

[0057] Finally, this invention provides processes for preparing theinstant compounds. These compounds can be prepared as shown below fromreadily available starting materials and/or intermediates followingprocesses well known in the art.

[0058] This invention will be better understood by reference to theExperimental Details that follow, but those skilled in the art willreadily appreciate that these are only illustrative of the invention asdescribed more fully in the claims which follow thereafter.Additionally, throughout this application, various publications arecited. The disclosure of these publications is hereby incorporated byreference into this application to describe more fully the state of theart to which this invention pertains.

EXPERIMENTAL DETAILS

[0059] A. Schemes and Syntheses

[0060] The synthesis of the claimed compounds is summarized in Scheme Iwherein H₁, H₂, R₁, R₂, R₃, R, R′, and R″ are as described hereinabove.

[0061] When R₁, is urea, compound 1 is reacted with an appropriatelysubstituted isocyanate in an organic solvent, preferably DCM(dichloromethane), THF (tetrahydrofuran), or DMF(N,N-dimethylformamide), at a temperature preferably between −78-120° C.to give compound 2. When R₁ is alkyl or heterocyclyl, compound 1 isreacted with an appropriate halide, tosylate, mesylate or the like in anorganic solvent such as DMF, DMSO (dimethyl sulfoxide), or acetone inthe presence of a base such as TEA (triethylamine), DIEA(diisopropylethylamine), and K₂CO₃ at a temperature preferably between10-150° C. When R₁ is aryl or heteroaryl, compound 1 is reacted with anappropriate halide, tosylate, mesylate or the like in the presence of anorganometalic catalyst such as Pd(Ac)₂ and Pd₂dba₃ (dba:dibenzylideneacetone), and a base such as TEA, DIEA, and K₂CO₃ in anorganic solvent such as THF, DMF, and DCM at a temperature preferablybetween 0-150° C. When R₁ is pyridine, pyrimidine, or other electrondeficient heterocycles, the reaction can be conducted in the absence ofthe organometalic catalyst. When R₁ is —C(O)R, —C(O)—C(O)R, compound 1is reacted with an appropriate carboxylic acid in the presence of acoupling reagent such as DCC (dicyclohexylcarbodiimide) and PyBrop(Bromo-tris-pyrrolidino-phosphonium hexafluorophosphate) in an organicsolvent such as DCM, THF, and DMF at a temperature preferably between0-80° C. Compound 1 can react with the acid halide of —C(O)R,—C(O)—C(O)R, —SO₂R, and —P(O)(OR′)(OR″) in the presence of a base suchas TEA, DIEA, and K₂CO₃ in an organic solvent such as DCM, THF, and DMFto give 2.

[0062] Compound 2 can react with compound 4 in an organic solvent suchas ethanol, DMF, DMSO, and toluene at a temperature preferably between50-150° C. to give the corresponding compound of formula I.Alternatively, compound 2 can be hydrolyzed with a base such as LiOH andNaOH to give compound 3. Compound 3 can then react with 4 in thepresence of a coupling reagent such as DCC and PyBrop in an organicsolvent such as THF, DMF, and dioxane to give the corresponding compoundof formula I.

[0063] The examples below describe in greater particularity the chemicalsynthesis of representative compounds of the present invention. Theremaining compounds disclosed herein can be prepared similarly inaccordance with one or more of these methods. No attempt has been madeto optimize the yields obtained in these reactions, and it would beclear to one skilled in the art that variations in reaction times,temperatures, solvents, and/or reagents could increase such yields.

Example 1 Compound (1)1-(3,3-Dimethyl-2-oxo-pentanoyl)-pyrrolidine-2-carboxylic acidN′-pyridine-2-yl-hydrazide

[0064] A mixture of(2S)-1-(1,2-dioxo-3,3-dimethylpentyl)-2-pyrrolidine-carboxylic acid (482mg, 2 mmol), prepared from L-proline methyl ester according to theprocedure described in WO 96/40633, 2-hydrazinopyridine (364 mg, 2mmol), PyBrop (932 mg, 2 mmol), DMAP (4-dimethyaminopyridine, 122 mg)and DIEA (4 mL) in THF (dry, 50 mL) was stirred at room temperature for24 h. Water and ethyl acetate were added. The organic phase was washedwith ammonium chloride solution, followed by brine, and dried withMgSO₄. Column chromatography (silica gel, ethyl acetate:methanol=10:0.5)gave a colorless oil; 490 mg (74%); MS (m/z) 333 (M+1); ¹H NMR (d₆-DMSO)δ0.85 (t, J=8 Hz, 3 H), 1.21 (s, 3 H), 1.23 (s, 3 H), 1.7 (m, 2 H), 1.90(m, 1 H), 2.10 (m, 2 H), 2.35 (m, 1 H), 3.49 (t, J=8 Hz, 2 H), 4.62 (m,1 H), 6.76 (m, 2 H), 7.51 (t, J=6 Hz, 1 H), 8.14 (d, J=6 Hz, 1 H).

[0065] Compounds (2)-(8) were synthesized in the manners similar to theabove example.

Example 2 Compound (9)1-(2-Oxo-2-thiophen-2-yl-acetyl)piperidine-2-carboxylic acidN′-(6-methyl-4-trifluoromethyl-pyridin-2-yl)-hydrazide

[0066] Intermediate 1: Methyl1-(1,2-Dioxo-2-methoxy)-2-piperidinecarboxylate

[0067] A solution of methyl pipecolinate hydrochloride (7.2 g, 40 mmol)in dry DCM (100 mL) and TEA (8.3 g) was cooled to 0° C. The slurry wasstirred for 1 h. Methyl oxalyl chloride was added. The mixture wasstirred at 0° C. for 2 h. Water was added, and the organic phase waswashed with a NaHCO₃ solution, dried with MaSO₄. Evaporation of thesolvent and drying in vacuum gave a reddish oil; 9.1 g (99%); MS (m/z)252 (M+Na).

[0068] Intermediate 2: Methyl1-[1,2-Dioxo-2-(thien-2-yl)ethyl)-2-piperidinecarboxylate

[0069] To a solution of Intermediate 1 (2.29 g, 10 mmol) in THF at −78°C., a solution of thienyllithium (1.0 M, 13 ml, 13 mmol) was addedslowly. The mixture was stirred at the same temperature for 4 h,quenched with ammonium chloride solution, extracted with ethyl acetate,and dried with MgSO₄. After evaporation of the solvent, a reddish oilwas obtained; 2.51 g (89%); MS (m/z) 304 (M+Na).

[0070] Intermediate 3:1-[1,2-Dioxo-2-(thien-2-yl)ethyl)-2-piperidinecarboxylic acid

[0071] Intermediate 2 (2.45 g, 8.72 mmol) was dissolved in MeOH (50 mL).LiOH solution (1 N, 13 mL) was added at 0° C., and the mixture wasstirred at the same temperature for 2 h and at room temperature for 16h. The reaction mixture was acidified with 1 N HCl, and extracted withethyl acetate. The organic phase was washed with brine and dried withMgSO₄. After evaporation of the solvent and drying under vacuum, ayellow solid was obtained, and was used for the next step withoutpurification.

[0072] Compound (9):1-(2-Oxo-2-thiophen-2-yl-acetyl)piperidine-2-carboxylic acidN′-(6-methyl-4-trifluoromethyl-pyridin-2-yl)-hydrazide

[0073] From Intermediate 3 (267 mg, 1 mmol),2-hydrazino-6-methyl-4-trifluoromethylpyridine (191 mg, 1 mmol), PyBrop(466 mg, 1 mmol), DMAP (122 mg) and DIEA (2 mL) in THF (30 mL), usingthe same procedure for Compound 1, the title compound was obtained as awhite solid; 110 mg (25%). MS (m/z) 441 (M+1).

Example 3 Compound (10) 2-Azetidinecarboxylic acid,1-[(phenylmethyl)sulfonyl]-, 2-(2-pyridinyl)hydrazide, (2S)-

[0074]

[0075] 1-Phenylmethanesulfonyl-azetidine-2-carboxylic acid methyl ester:

[0076] Azetidine-2-carboxylic acid (560 mg, 5.5 mmoles) was suspended inmethanol (25 mL) and cooled to −5° C. under an argon atmosphere. Thionylchloride was added dropwise and the mixture was allowed to warm to roomtemperature over a 3 hour period. After concentration in vacuo, theresidue was dissolved in dry dichloromethane (25 mL) and treatedsequentially with benxzyl sulfonyl chloride (1.17 g, 6.14 mmoles) anddiisopropylethylamine (2.15 mL, 12.3 mmoles). After stirring overnight,the mixture was concentrated and purified by flash chromatography onsilica gel to afford 1.13 g (76%) of the product as a colorless oil. ¹HNMR (CDCl₃) δ2.29-2.51 (m, 2H); 3.21-3.29 (m, 1H); 3.81 (s, 3H); 4.02(q, 1H, J=8.6); 4.32 (d, 1H, J=14.6); 4.46 (d, 1 H, J=14.6); 4.86 (dd,1H, 9.4, 8.6); 7.34-7.43 (m, 3H); 7.46-7.54 (m, 2H).

[0077] 1-Phenylmethanesulfonyl-azetidine-2-carboxylic acid:

[0078] 1-Phenylmethanesulfonyl-azetidine-2-carboxylic acid methyl ester(1.13 g, 4.19 mmoles) was dissolved in methanol (20 mL) and cooled to 0°C. Treatment of this solution with aqueous lithium hydroxide (7.75 mL, 1M) was followed by warming to ambient temperature over a 3 hour period.Most of the methanol was removed in vacuo and the pH was adjusted to 1by treatment with 1 M HCl. The product was extracted into ethyl acetate,dried over anhydrous sodium sulfate and concentrated to afford 886 g(83%) of the product as a white solid. ¹H NMR (CDCl₃) δ2.37-2.57 (m,2H); 3.21-3.31 (m, 1H); 3.81 (s, 3H); 4.01 (q, 1H, J=8.6); 4.33 (d, 1H,J=13.7); 4.44 (d, 1 H, J=13.7); 4.98 (dd, 1H, 9.4, 8.6); 7.34-7.53(series of m, 5H).

[0079] 1-Phenylmethanesulfonyl-azetidine-2-carboxylic acidN′-pyridin-2-yl-hydrazide:

[0080] 1-Phenylmethanesulfonyl-azetidine-2-carboxylic acid (142 mg, 0.56mmoles) was dissolved in dry dichloromethane (10 mL) and treated withpyridin-2-yl-hydrazine (60 mg, 0.55 mmoles), diisopropylcarbodiimide(0.09 mL, 0.57 mmoles), camphorsulfonic acid (44 mg, 0.19 mmoles), andDMAP (23 mg, 0.19 mmoles). After stirring overnight at room temperature,the solution was concentrated and purified by flash chromatography onsilica gel to afford 16 mg (8%) of the product as a yellow foam. ¹H NMR(CDCl₃) δ2.36-2.47 (m, 2H); 3.43-3.52 (m, 1H); 3.93 (q, 1H, J=10.3);4.33 (q, 2H, J=13.7); 4.83 (t, 1 H, J=8.6); 6.53 (d, 1H, J=8.6);6.70-6.77 (m, 1H); 6.85 (br s, 1H); 7.26-7.54 (series of m, 6H); 8.11(d, 1H, J=6.0); 8.36 (br s, 1 H).

[0081] B. Assays

[0082] Results from Example 6 are shown in Table 1. Examples 5 and 6detail the methods used for preparation of the cell cultures used inExample 7.

Example 5 Dorsal Root Ganglion (DRG) Culture

[0083] DRG were dissected from newborn or 1-day-old CD rats and placedinto PBS on ice. After rinsing twice with sterile plating medium, DRGwere transferred to empty wells of a 6-well plate coated withpolyornithine/laminin (Becton Dickinson Labware) using #7 curvedforceps. Three ml/well of plating medium was then added very gently, soas not to disturb the DRG. Plating medium is Leibovitz's L-15 medium(Gibco), plus 0.6% glucose, 33 mM KCl, 10% FCS, 10 mM Hepes andpenicillin/streptomycin/glutamine. After overnight incubation at about37° C. in 5% CO₂, this medium was replaced with 3 mL/well of assaymedium [Leibovitz's L-15 medium plus 0.6% glucose, 1% FCS, 1% N-2supplement (Gibco), 10 μM ara-C, 10 mM Hepes, andpenicillin/streptomycin/glutamine] containing either vehicle (DMSO,1/200,000), positive control (2-4 ng/mL NGF) or test compound (50-250nM). All media were prepared fresh daily. DRG were microscopicallyexamined for neurite outgrowth on days 1-5. Under optimal conditions,vehicle treatment did not induce neurite outgrowth from DRG. Anexperiment was considered positive (+) if the instant compound inducedneurites of ≧1 diameter of the DRG.

Example 6 Primary Rat Hippocampal Cells

[0084] Hippocampal cells were dissected from the brains of embryonic day18 rat pups and dissociated with trypsin (1 mg/mL) and trituration.Cells were seeded at 30,000 cells/well in 96-well plates filled with 100μL MEM and 10% FBS. At 7 days in culture, cells were fixed with 4%paraformaldehyde and immuno-fluorescence was performed.

Example 7 Human M17 Neuroblastoma Cells

[0085] M17 human neuroblastoma cells were cultured in 1:1 ratio of EMEMand Ham's F12 with 1×NEAA and 10% FBS. The culture media contained 1×PSNantibiotic and was exchanged every other day, and the cells were passedin log phase near confluence. TABLE 1 In Vitro Neurotrophic ActivityCompound No. Structure MS (M + 1)+ Rat Hippocampal Cell Response (1)

333 157 (2)

383 107 (3)

410 106 (4)

415 105 (5)

395 <100 (6)

415 <100 (7)

429 <100 (8)

435 106 (9)

441 118 (10)

347 115

Example 8 Neurite Outgrowth Assay

[0086] Cultures were incubated with normal horse serum (1:50; VectorLabs) for about 20 min, rinsed and then incubated with primary antibody,microtubule associated-protein 2 (anti-mouse MAP-2; 1:1000; Chemicon)for about 2 h at about RT. Following primary antibody, cultures wererinsed and incubated with fluorescein anti-mouse IgG (rat absorbed;1:50; Vector Labs) for about 1 h. After fluorescein incubation, thecultures were rinsed and read in PBS on a fluorescent plate reader(excitation: 485 nm; emission: 530 nm). A compound was regarded asactive if the neurite outgrowth response was greater than the meanDMSO-treated control response on the same plate. The response to testcompound was reported as percent of DMSO-treated control. Thesignal-to-noise separation was consistent: the fluorescence from DMSOcontrol wells is at least two-fold greater than blank wells.

[0087] While the foregoing specification teaches the principles of thepresent invention, with examples provided for the purpose ofillustration, it will be understood that the practice of the inventionencompasses all of the usual variations, adaptations and/ormodifications as come within the scope of the following claims and theirequivalents.

What is claimed is:
 1. A compound of Formula I,

or a pharmaceutically acceptable salt thereof, wherein H₁ is selectedfrom the group consisting of a 4-membered nitrogen-containingheterocyclyl having 3 carbon ring atoms, a 5-memberednitrogen-containing heterocyclyl having 0 or 1 additional heteroatomring member selected from O, S, and N, and a 6- or 7-memberednitrogen-containing heterocyclyl having 0, 1, or 2 additional heteroatomring members selected from O, S, and N; H₂ is a 5- or 6-memberedheteroaryl; R₁ is selected from urea, C₁-C₁₀ alkyl, aryl, heteroaryl,heterocyclyl, —C(O)R, —C(O)—C(O)R, —SO₂R, and —P(O)(OR′)(OR″), whereinR, R′, and R″ are independently selected from the group consisting ofalkyl, aryl, heteroaryl, and heterocyclyl; and R₂ and R₃ areindependently hydrogen or C₁-C₁₀ alkyl.
 2. The compound of claim 1having the structure of Formula Ia,

wherein H_(2a) is a 5- or 6-membered heteroaryl and wherein X is aheteroatom selected from O, S, and further wherein N, and R₁, R₂, R₃,and H₁ are as claimed in claim
 1. 3. The compound of claim 1, having thestructure of Formula Ib,

wherein R₁, R₂, R₃, H₁, and H₂ are as claimed in claim
 1. 4. Thecompound of claim 3, wherein H₂ is attached at a β-carbon atom.
 5. Thecompound of claim 3, wherein R₁ is selected from the group consisting ofC₁-C₁₀ alkyl, aryl, heteroaryl, heterocyclyl, —C(O)R, —C(O)—C(O)R, and—SO₂R.
 6. The compound of claim 5, wherein R₁ is selected from the groupconsisting of —C(O)R, —C(O)—C(O)R, and —SO₂R wherein R is selected fromthe group consisting of aryl, heteroaryl, cycloalkyl, and C₄-C₁₀straight or branched alkyl.
 7. The compound of claim 1 which is1-(3,3-dimethyl-2-oxo-pentanoyl)-pyrrolidine-2-carboxylic acidN′-pyridine-2-yl-hydrazide.
 8. The compound of claim 1 which is1-(2-oxo-2-thiophen-2-yl-acetyl)piperidine-2-carboxylic acidN′-(6-methyl-4-trifluoromethyl-pyridin-2-yl)-hydrazide.
 9. The compoundof claim 1 which is 2-azetidinecarboxylic acid,1-[(phenylmethyl)sulfonyl]-, 2-(2-pyridinyl)hydrazide, (2S)-.
 10. Apharmaceutical composition comprising the compound of claim 1 and apharmaceutically acceptable carrier.
 11. A method of treating a subjectsuffering from a condition characterized by neuronal damage caused bydisease or trauma, which method comprises administering to the subject atherapeutically effective dose of pharmaceutical composition of claim10.
 12. A method of inhibiting in a subject the onset of a conditioncharacterized by neuronal damage caused by disease or trauma, whichmethod comprises administering to the subject a prophylacticallyeffective dose of pharmaceutical composition of claim
 10. 13. The methodof claim 11 or 12, wherein the condition is caused by trauma to any partof brain, spinal cord or peripheral nerve.
 14. The method of claim 11 or12, wherein the condition is selected from the group consisting ofParkinson's disease, Alzheimer's disease, stroke, multiple sclerosis,amyotrophic lateral sclerosis, peripheral neuropathy, and Bell's palsy.15. The method of claim 14, wherein the condition is Parkinson'sdisease.
 16. The method of claim 14, wherein the condition isAlzheimer's disease.
 17. The method of claim 14, wherein the conditionis diabetic neuropathy.
 18. A method of stimulating neuronal growthcomprising contacting neurons with an effective amount of the compoundof claim
 1. 19. A process for preparing the compound of Formula I,

which process comprises: (a) converting compound 1 to compound 2; and

(b) reacting compound 2 with compound 4 to form the compound 1.